From DoomWiki.org

The cyberdemon is a towering, hellish marriage of demon flesh and technology, with a gigantic muscular stature, a minotaur-like head with prominent black and gray horns, a gored humanoid torso filled with red wiring, a metallic prosthetic right leg, and a large rocket launcher mounted on its left arm. By far the most formidable enemy in classic Doom, and one of the most intimidating boss monsters in video game history, it is more than capable of taking out a healthy player in one hit from its arm-grafted weapon.

This monster first appears as a boss at the end of Doom level E2M8, and re-appears in the secret level E3M9. In the Ultimate Doom expansion, it makes additional appearances on E4M2, E4M6, and E4M7. The cyberdemon is featured on the retail box cover of Doom II, and it appears sparingly throughout the single-player game. It occurs on a large number of levels during cooperative multiplayer, however. The manual for the PC version of Doom II describes the monster as such:

"Half unfeeling machine, half raging horned devil. This walking nightmare has a rocket launcher for an arm and will definitely reach out and touch you. Make sure you're loaded for bear before you get to this guy."

A cyberdemon will let out a loud animalistic, bovine-like roar when it spots a player - loud enough to be heard no matter how far away it is from the player. It attacks by firing barrages of three rockets. It has 4000 hit points and does not receive splash damage from explosions, making it fairly difficult to kill. It is also the fastest moving monster in the original game (the lost soul's charge attack not withstanding), and second fastest in Doom II (after the arch-vile). When destroyed, the cyberdemon's body will instantly dissolve into voluminous reddish clouds of flesh, blood and gore, leaving only his blood-soaked hooves; as he explodes, he lets out a short roar that is abruptly interrupted by the sound of his body exploding.

The cyberdemon's rockets are the same as the player's rockets; however as all projectiles shot by monsters, they do not damage other monsters of the same type. Furthermore, the cyberdemon and the spiderdemon take only direct hit damage, and are immune to all blast damage. Therefore, a greater number of rockets is required to kill these bosses than might be expected, and they must be direct hits. The cyberdemon is given a higher probability of performing his attack than other monsters, causing him to launch volleys of rockets at a high frequency. In common with other monsters, although the cyberdemon is shown with his rocket launcher in his left hand, the rockets emerge from his middle. While the cyberdemon does not have a melee attack in the PC and Doom 64 games, an apparently unintentional one does exist in the Super NES port: if the player is close enough to one in this version of the game, its attack consists of the rocket firing animation, but a scratching sound is heard with no rocket being fired.

Killing a cyberdemon is almost impossible without using a large amount of ammunition. The BFG9000 is the most effective weapon against a cyberdemon, although the plasma gun can work fairly well. Three to four direct BFG hits will usually kill a cyberdemon, and at point-blank range two well-placed shots are enough. If a BFG9000 is not available, the rocket launcher is also effective - but be prepared for a long fight, since around 45 well-placed hits with the rocket launcher is required to kill a cyberdemon. Killing a cyberdemon with other weapons is significantly more difficult: for example it takes around 400 bullets from a chaingun. It is extremely difficult to kill a cyberdemon with melee attacks and it takes roughly 400 chainsaw or non-berserkfist hits to do so, but given their extreme powers and low pain chances, it is strongly not recommended under most circumstances. Almost certainly because of the difficulty involved, the Xbox Live Arcade release of Doom II features an Achievement that requires the player to kill a cyberdemon with their bare hands, named "You Have Huge Guts", after an infamous phrase from the Doom comic.

Because a cyberdemon has a low pain chance, it is difficult to prevent it from attacking. It is also important to be constantly aware of when it fires a rocket, as it will do so relentlessly. Circle-strafing can be used to avoid return fire while attacking. Because one rocket will often be enough to critically injure the player, it is imperative that all rockets are avoided. Because of splash damage, it is also important to stay away from the explosions. For example, it is advisable to avoid standing too close to a wall when fighting a cyberdemon, as splash damage can be sustained from rockets hitting the wall.

A skilled player can somewhat nullify the cyberdemon's low pain chance by straferunning towards it to get within point blank range, and then hitting it with the super shotgun. The monster will flinch roughly eighty percent of the time when hit by the full twenty-pellet blast, giving the player time to retreat, reload, and repeat the process. This can take the cyberdemon down in fewer than 25 shots, but is very risky, and only recommended in areas where the rocket launcher is impractical, or to conserve rocket and cell ammunition. This tactic is common amongst high tier speedrunners.

The cyberdemon's immense size can sometimes be used as an advantage when attacking it. In some maps, the cyberdemon(s) are placed in a large courtyard or structure and the entrance is too small for them to pass through. This can help a novice player to escape if major injuries are sustained.

Due to its firepower and hitpoints which are by far the highest among demons, the cyberdemon easily dominates in monster infighting battles. Because of this, luring it into fighting another monster is a great way to save ammunition. However, it can occasionally get overwhelmed by either the spiderdemon (as often occurs in MAP20: Gotcha!) or a large group of very strong demons like the Baron of Hell (see MAP08: Tricks and Traps).

It is impossible to provoke infighting between two cyberdemons, as they are unaffected by the splash damage from each others' rockets. There is no map in Doom and Doom II where the player would encounter two or more cyberdemons at the same time, however, so this was probably never taken into consideration.

The cyberdemon is portrayed with a prominent human-like nose in the Doom II title screen, based on art by Gerald Brom. However, in the sprites and the original sculpture by Adrian Carmack, the cyberdemon only has two simple nostrils.

By default, all projectiles are spawned 32 map units above the center of the shooter (although this has been changed in Doom 64). The cyberdemon is the monster for which this behavior is most noticeable, as the rockets fired by the cyberdemon appear to spawn near the space between its legs.

The cyberdemon's left (natural) leg audibly impacts upon the ground; no other monster has audible footsteps. The cyberdemon's other artificial leg also makes noise as it moves, the same sound made by the mechanical legs of the spiderdemon.

Normally when a level is finished, for example by pressing a switch, the screen melt effect takes place instantly. However, if the level is meant to end after killing the cyberdemon or spiderdemon, an extra delay of 30 tics occurs, coded into the monsters' state sequences in order to afford the player a chance to look at the monster's corpse. Consequently, in the Doom II cast sequence, the corpses remain noticeably longer on the screen in comparison with the other characters.

The cyberdemon, along with the demon, mancubus, and spiderdemon, is one of the few monsters whose dying sound clips includes noise other than the monsters' vocals; in this case, the cyberdemon's roar is accompanied by a loud explosion and is cut off by it near the end as its body completely disintegrates.

The cyberdemon is depicted in the game as an ungulate: it stands on the very tips of its toes, which have fused to become hooves. Ungulates are distinguished from digitigrades, such as cats, dogs, and birds, which stand with their toes flat on the ground but their heels off the ground; and plantigrades, like humans and bears, which stand with their heels flat on the ground.

In the Doom novels, in which monsters are generally not referred to by their in-game names, the cyberdemon's mechanical parts are said to be steam powered, leading the characters to call them "steam demons."

The horned skull near the top of the door texture BIGDOOR7 resembles the cyberdemon's head. It is unclear if this is merely a decoration or the skull of an actual fallen cyberdemon.

The Depths of Doom Trilogy's manual erroneously states the cyberdemon is only present in Doom II, due to it not being mentioned in the original game's manual.

This table assumes that all calls to P_Random for damage, pain chance, blood splats, and bullet dispersal are consecutive. In real play, this is never the case: counterattacks and AI pathfinding must be handled, and of course the map may contain additional moving monsters and other randomized phenomena (such as flickering lights). Any resulting errors are probably toward the single-shot average, as they introduce noise into the correlation between the indices of "consecutive" calls.

Assumes that the target takes a direct hit from each shot.

Assumes that direct hits are possible, which does not occur in any stock map.

The cyberdemons in Doom 64 have not gone through many changes except that they have darker colored skin, are slightly stronger and much larger. The Doom 64 version of the cyberdemon is notable for having the ability to lead its shots, making it an even more formidable opponent; the cyberdemon's third rocket is usually fired at the player's anticipated position rather than the player's current position. The rockets also leave smoke trails and fly out much faster. The cyberdemons' rockets in this game emerge from the launcher itself instead of the middle. While they have the same death sequence animation as their PC counterpart, for the most part (full-body explosion), it is more elaborate in Doom 64, involving its form stricken with several separate explosions before the body essentially evaporates in a haze of fiery blood, replete with a shot of its skeletal frame vanishing with it.

Cyberdemons are relatively rare throughout the game, appearing chiefly in the secret levels or later in the game.

A special variety of cyberdemon appears on the game's introductory title sequence map. This particular cyberdemon is coded to only ever fire rockets toward the position of the cinematic moving camera and will not infight with other monsters, nor will it react to the player if the game is hacked to allow visiting MAP33. It can be killed, but since it has no death frames it will simply disappear.

The cyberdemon was originally known as the Harbinger of Doom. During World War II, he was summoned at Castle Wolfenstein by the Axis army. B.J. Blazkowicz was able to defeat it with the Spear of Destiny, destroying its right leg and left arm. The Harbinger of Doom vowed that it would have a rematch with Blazkowicz's descendent in the future. The rematch happened in Doom II RPG.